1. Field of Invention
The present invention relates to a porcelain enamel coating having a metallic appearance. More particularly, the present invention relates to a composition containing a glass component and metal particles that when fired forms a porcelain enamel coating having a metallic appearance, a method of forming a porcelain enamel coating having a metallic appearance and articles having a surface provided with a porcelain enamel coating having a metallic appearance.
2. Description of Related Art
Porcelain enamel coatings have long been used to protect metal surfaces from abrasion, corrosion and other chemical and mechanical damage. Through the use of various pigments, coloring oxides and mill additions, it is possible to form decorative porcelain enamel coatings in a wide variety of colors, textures and glosses. However, prior art efforts to formulate porcelain enamel coatings having a metallic appearance have generally not met with success.
Metal particles have been added to porcelain enamel compositions in the past to form composite xe2x80x9ccermetxe2x80x9d coatings. As noted in Mumford et al., U.S. Pat. No. 4,555,415, the addition of metal particles, and in particular aluminum particles, to conventional porcelain enamel coating compositions results in enamels that are prone to xe2x80x9cfoamingxe2x80x9d during their preparation, producing porous coatings. In some applications, such as the interior surface of oven cavities, such porous coatings can provide certain advantages. However, where the enamel is intended to provide a decorative coating that also protects the underlying surface from chemical and mechanical wear, such porosity is generally considered to be a disadvantage.
The present invention provides a composition for use in forming a porcelain enamel coating having a metallic appearance. The composition according to the invention preferably comprises a low shear blend of a glass component comprising at least one glass frit that fuses at a temperature of less than about 600xc2x0 C. and metal particles such as aluminum, nickel, copper and stainless steel. Upon firing at a temperature of from about 535xc2x0 C. to about 600xc2x0 C., the composition forms a non-porous vitreous porcelain enamel coating that has a metallic appearance, which through the incorporation of various optional pigments and/or mill additions, can range from a bright brushed nickel or stainless steel appearance to matte dark metallic finish.
In the preferred embodiment of the invention, the glass component comprises one or more glass frits comprising by weight from about 25% to about 45% SiO2, from about 8% to about 30% TiO2, from about 20% to about 40% Na2O+K2O+Li2O, from about 0% to about 20% B2O3, from about 0% to about 8% Sb2O5, from about 0% to about 7% P2O5, from about 0% to about 15% V2O5, and from about 0% to about 6% BaO. Metal oxides such as oxides of cobalt, copper, manganese, nickel, iron and chrome, can be smelted into the glass to improve adhesion of the fired porcelain enamel coating to certain metal surfaces and/or to tint the resulting color of the fired porcelain enamel coating. Such a glass frit will fuse at a firing temperature of from about 535xc2x0 C. to about 600xc2x0 C. The preferred metal particles for use in the invention are aluminum flakes, but various other particle forms and/or metals such as copper, nickel and stainless steel can also be used.
The present invention also provides a method of forming a porcelain enamel coating having a metallic appearance and articles having a surface provided with a porcelain enamel coating having a metallic appearance. The method according to the invention comprises blending a glass component comprising at least one glass frit that fuses at a temperature of less than about 600xc2x0 C. and metal particles together at low shear to form a porcelain enamel composition, applying the porcelain enamel composition to the surface, and firing the porcelain enamel composition at a temperature of from about 535xc2x0 C. to about 600xc2x0 C. to form the porcelain enamel coating.
The foregoing and other features of the invention are hereinafter more fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the present invention may be employed.